1. Department of Physics, University of Oslo, P.O. Box 1048, Blindern, 0316 Oslo, Norway
2. Department of Physics and Technology, University of Tromsø, P.O. Box 6050, Langnes, 9037 Tromsø, Norway
3. National Institute of Maritime, Port, and Aviation Technology, 6-38-1, Shinkawa, Mitaka-shi, Tokyo 181-0004, Japan